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Keeping electronic devices cool is important when considering both their function and durability, as temperature influences material properties and energy flow. The temperature of "hot spots" that can be detected affects the performance of various technologies, from smartphones to electric vehicles. The ability for devices to work at faster speeds has stalled in recent years since adding more power to them has resulted in overheating.

When examining heat transport at the nanoscale level, challenges arise due to heat behaving fundamentally differently at tiny scales and the inadequacy of traditional heat-flow models to predict the behavior. One of the challenges arises from the difficulty in predicting or measuring how vibrational energy moves in three dimensions at these scales.

Two competing theories attempt to explain this behavior: ballistic flow and hydrodynamic flow. In the ballistic theory, heat behaves similarly to light, with heat-carrying particles (phonons) bouncing around erratically. In the hydrodynamic theory, heat is treated more like a flowing fluid and phonons move in a concerted manner.

A research team from the University of Colorado, Utah State University and Carnegie Mellon University, with the involvement of Albert Beardo, lecturer in the UAB Department of ÌÇÐÄÊÓƵics, examined these two theories and compared computational predictions with real-world experiments.

Although the two models are conflicting in their nature, the research analysis recently in npj Computational Materials advocates for a combination of the theories to better understand heat flow in nanoscale systems.

"In order to build faster and more sustainable technologies, we need to develop a better way of approaching thermal management," said Ismaila Dabo, researcher at Carnegie Mellon University and coordinator of the study.

According to UAB lecturer Beardo, first author of the article, "There is a need to develop simple models that focus on capturing the most significant physical phenomena constraining thermal relaxation, rather than aiming for computationally intractable models that describe the mechanical evolution of systems in full detail."

In future studies on how these models can best be incorporated together, comparisons of the two frameworks through simulations that take into account the interaction between electrons and phonons may be key to creating better theories. The research highlights "the need to develop experimental thermal measurement techniques that can directly map heat flow in complex three-dimensional geometries with nanometer spatial resolution and picosecond temporal resolution."